In the field of electronic design, amplifier circuits, such as a class-D amplifier, are commonly used to convert a given input signal to a similar signal of a greater magnitude. Amplifier circuits can typically only operate within a given input signal magnitude range, beyond which the amplifier circuit, or other associated circuitry, can be damaged by an over-current condition. Circuit designers of amplifier circuits often design safeguards or limitations into the amplifier circuits, thus providing warnings or otherwise preventing the occurrence of over-current conditions.
To detect an over-current condition in an amplifier circuit, circuit designers often generate a reference voltage to compare with the output voltage of the amplifier circuit. The reference voltage that is compared with the output voltage of the amplifier is derived from circuitry that is separate from the amplifier circuit. However, this reference voltage does not take into account process variations that may result in the manufacture of a power field-effect transistor (FET) of the amplifier circuit, such as variations in temperature or the drain-to-source resistance RDSon of the power FET. These manufacturing variations may result in inaccurate detection of an over-current condition. This reference voltage is also a static specification dictated by the manufacturer, and is not subject to change to suit the needs of the end-user of the amplifier circuit. Additionally, voltage spikes that result from inrush current at activation and deactivation of the power FET may cause false over-current detection, thus undesirably shutting off the amplifier circuit at inappropriate times.